Generally, in such networks so-called Quality of Service (QoS) has to be supported for certain packets (in the following simply referred to as packets) transported in a packet data network (in the following referred to as packet network).
The term Quality of Service (QoS) relates especially to the quality of transmission of the packets. For example, in case that speech signals are transmitted in form of packet (as in GSM, for example), it is necessary that these packets are processed in real-time. Therefore, these packets require a fast transmission without delay. On the other hand, there are packets which do not require a real-time processing, for example in a computer network without real-time applications or in GPRS (General Packet Radio Service).
This is especially important in the field of internet telephony (IP telephony) since in such a network a lot of packets are transported which do not require a real-time processing since they comprise text data, for example. These packets can be transported with a certain delay, since a delay usually does not affect the transmission quality of such data. In contrast thereto, if speech signals transported in packets would be transported with a certain delay, the quality of transmission would be remarkably reduced. Therefore, a certain quality has to be secured for the transmission of a packet network.
Currently, there exist two main approaches for providing Quality of Service in IP networks. The first approach is called Integrated Services. According to this approach, IP packets are flowing inside flows for which well defined, i.e., guaranteed resources are allocated.
The second approach is called Differentiated Services (DiffServ) and it is based on the idea that packets are indicated as needing different kind of processing inside the network. That is, the packets are classified. Hence, in contrast to Integrated Services, Differentiated Services give relative guarantees.
Thus, routers in a network which support Differentiated Services have to distinguish between different classes of packets in order to forward them in the way as required. Therefore, in Differentiated Services each packet has a special control data field (a so-called DS field or Differentiated Services field) comprising IP TOS bits (IP type of service bits). In this field, the kind of processing needed by the corresponding packet is indicated by a certain value. That is, the IP TOS bits define the so-called “per-hop behaviour” (PHB) of the packet.
FIG. 7 shows the basic structure of such a packet. As illustrated, the packet comprises the IP header in which the DS field including the IP TOS bits is arranged and a packet body including the data to be transmitted in this packet.
When a packet which does not comprise the above mentioned DS field enters a network which supports Differentiated Services, such a field has to be included in the packet. For example, packets transmitted via a GSM network (real-time packets) have to be indicated as needing a real-time processing. This addition is performed by so-called edge routers. Thus, the edge routers represent a kind of interface between the packet network supporting Differentiated Services and other packet networks.
An example of such a network is schematically illustrated in FIG. 1. A network NW comprises core routers R11, R12 and R13 which transmit packets only within the packet network NW. The network NW supports Differentiated Services. That is, each of the core routers is able to read the IP TOS bits and to treat each respective packet correspondingly.
Furthermore, edge routers ER1 and ER2 are provided. The edge router ER1 connects the network NW to a telephone network TN in which only speech signals are transmitted. The telephone network TN could be a GSM network, for example, in which packets (speech) require a real-time processing. On the other hand, the edge router ER2 connects the network NW to a computer network CN in which only packets are transmitted which do not require a real-time processing.
By the edge routers ER1 and ER2 it has to be determined which kind of service for the packets entering the network NW from the respective network CN or TN has to be provided. In the above example, the telephone network is a GSM network. Hence, the service required for packets entering from the telephone network TN has to be a real-time processing. Thus, the packets have to be indicated accordingly. While the packets are transmitted through the network NW, the routers R11, R12 and R13 have to check the IP TOS bits of the packets in order to adequately treat the packets and to transmit them accordingly. It should be noted that in order to simplify the illustration, further connections to the outside of network NW are only indicated by arrows. This connections could be connected to further networks, computer terminals or telephones etc.
Thus, the above method using the Differentiated Services has the drawback that a special control data field comprising the IP TOS bits has to be included in each packet. Therefore, the processing load in the network is increased. Furthermore, edge routers are necessary. Thus, additional hardware and software has to be provided. Moreover, in order to classify the packets, the control data field has to be investigated by the routers, which causes a complicated handling of the packets leading to a further delay of transmission.
In addition, in several routers according to the prior art it is not only referred to the DS field of a packet in order to classify this packet, but also to other information included in the packet. For example, this can be a protocol field, source and/or destination number, source and/or destination IP address, device interface etc. At least some of this information is not accessible in case the data of the packet is encrypted. This is for example the case in legacy IP devices.